1. Field of the Invention
The present invention relates to a wireless (radio) communication system for providing wireless communication services and a wireless (radio) terminal, and more particularly, to a method for informing, by the wireless communication system, to the terminal about information required for reception when the wireless terminal is connected to the wireless communication system, in which a base station updates system information according to a preset period, and the terminal efficiently receives or checks any update of the system information based on the period.
2. Description of the Related Art
FIG. 1 shows an exemplary network structure of an Evolved Universal Mobile Telecommunications System (E-UMTS) as a mobile communication system to which a related art and the present invention are applied. The E-UMTS system is a system that has evolved from the UMTS system, and its standardization work is currently being performed by the 3GPP standards organization. The E-UMTS system can also be referred to as a Long-Term Evolution (LTE) system.
The E-UMTS network can roughly be divided into an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) and a Core Network (CN). The E-UTRAN generally comprises a terminal (i.e., User Equipment (UE)), a base station (i.e., eNode B), and an Access Gateway (AG) that is located at an end of the E-UMTS network and connects with one or more external networks. The AG may be divided into a part for processing user traffic and a part for handling control traffic. Here, an AG for processing new user traffic and an AG for processing control traffic can be communicated with each other by using a new interface. One eNode B may have one or more cells. An interface for transmitting the user traffic or the control traffic may be used among the eNode Bs. The CN may comprise an AG, nodes for user registration of other UEs, and the like. An interface may be used to distinguish the E-UTRAN and the CN from each other.
Radio interface protocol layers between the terminal and the network can be divided into a first layer (L1), a second layer (L2) and a third layer (L3) based on three lower layers of an Open System Interconnection (OSI) standard model widely known in communications systems. A physical layer belonging to the first layer provides an information transfer service using a physical channel. A Radio Resource Control (RRC) layer located at the lowest portion of the third layer controls radio resources between the terminal and the network. For this purpose, the RRC layer allows RRC messages to be exchanged between the terminal and the network.
FIGS. 2 and 3 show radio interface protocol architecture between a terminal and E-UTRAN based on 3GPP radio access network standards. Particularly, FIG. 2 shows radio protocol architecture in a control plane, and FIG. 3 shows radio protocol architecture in a user plane.
The radio interface protocol in FIGS. 2 and 3 has horizontal layers comprising a physical layer, a data link layer and a network layer, and has vertical planes comprising a user plane for transmitting user traffic and a control plane for transmitting control signals. The protocol layers in FIGS. 2 and 3 can be divided into a first layer (L1), a second layer (L2) and a third layer (L3) based on three lower layers of an Open System Interconnection (OSI) standard model widely known in communications systems. Hereinafter, each layer in the radio protocol control plane in FIG. 2 and a radio protocol user plane in FIG. 3 will be described.
A first layer, as a physical layer, provides an information transfer service to an upper layer using a physical channel. The physical layer is connected to its upper layer, called a Medium Access Control (MAC) layer, via a transport channel. The MAC layer and the physical layer exchange data via the transport channel. Data is transferred via a physical channel between different physical layers, namely, between the physical layer of a transmitting side and the physical layer of a receiving side. The physical channel is modulated based on an Orthogonal Frequency Division Multiplexing (OFDM) technique, and utilizes time and frequency as radio resources.
The MAC layer located at the second layer provides a service to an upper layer, called a Radio Link Control (RLC) layer, via a logical channel. The RLC layer of the second layer supports reliable data transmissions. The function of the RLC layer may be implemented as a functional block in the MAC layer. In this case, the RLC layer may not exist. A Packet Data Convergence Protocol (PDCP) layer of the second layer, in the radio protocol user plane, is used to efficiently transmit IP packets, such as IPv4 or IPv6, on a radio interface with a relatively narrow bandwidth. For this purpose, the PDCP layer reduces the size of an IP packet header which is relatively great in size and includes unnecessary control information, namely, a function called header compression is performed.
A Radio Resource Control (RRC) layer located at the lowest portion of the third layer is only defined in the control plane. The RRC layer controls logical channels, transport channels and physical channels in relation to establishment, re-configuration and release of Radio Bearers (RBs). Here, the RB signifies a service provided by the second layer for data transmissions between the terminal and the E-UTRAN. If an RRC connection is established between the RRC layer of the terminal and the RRC layer of the radio network, the terminal is in the RRC connected mode. Otherwise, the terminal is in an RRC idle mode.
A Non-Access Stratum (NAS) layer located at an upper portion of the RRC layer performs functions, such as session management, mobility management and the like.
One cell constructing an eNB is set to one of bandwidths of 1.25 MHz, 2.5 MHz, 5 MHz, 10 MHz, 20 MHz and the like, so as to provide downlink or uplink transmission services to multiple terminals. Here, different cells may be set to provide different bandwidths.
Downlink transport channels for transmitting data from a network to a terminal may comprise a Broadcast Channel (BCH) for transmitting system information, a Paging Channel (PCH) for transmitting paging messages and a downlink Shared Channel (SCH) for transmitting other user traffic or control messages. Traffic or control messages of a downlink point-to-multipoint service (multicast or broadcast service) may be transmitted either via a downlink SCH, or via a separate downlink Multicast Channel (MCH). In addition, uplink transport channels for transmitting data from a terminal to a network may comprise a Random Access Channel (RACH) for transmitting an initial control message and an uplink Shared Channel (SCH) for transmitting user traffic or control messages.
Logical channels which are located at an upper portion of transport channels and mapped to the transport channels include a Broadcast Control Channel (BCCH), a Paging Control Channel (PCCH), a Common Control Channel (CCCH), a MBMS point-to-multipoint Control Channel/Multicast Control Channel (MCCH), a MBMS point-to-multipoint Traffic Channel/Multicast Traffic Channel (MTCH), and the like.
FIG. 4 shows a transmission on a control channel according to the related art.
A physical channel is composed of multiple sub-frames arranged on a time axis and multiple sub-carriers arranged on a frequency axis. Here, a single sub-frame includes a plurality of symbols on the time axis. One sub-frame is composed of a plurality of resource blocks, each of which includes a plurality of symbols and a plurality of sub-carriers. Also, each sub-frame can use particular sub-carriers of particular symbols (e.g., a first symbol) at the corresponding sub-frame for a Physical Downlink Control Channel (PDCCH), namely, a L1/L2 control channel. One sub-frame is a time duration of 0.5 ms. A Transmission Time Interval (TTI) as a unit time for which data is transmitted is 1 ms corresponding to two sub-frames.
In E-UMTS system, radio resource(s) of in a cell is allocated for an uplink radio resource(s) and a downlink radio resource(s). The base station (eNode B) is in charge of controlling or allocating of the uplink and downlink radio resource(s). Namely, the base station decides which terminal can use which or how much radio resource(s) for which particular time period(s). After such determination is made, the base station transmits those information to a corresponding terminal so that the terminal can perform the uplink or downlink transmission according to the information.
In conventional art, the terminal continuously uses the radio resource(s) in a connected mode. However, in recent years, there are many service based on an IP (Internet Protocol) packet, and continuously using of the radio resource(s) in the connected mode may cause a drawback because these IP packet based service does not always communicates packet(s) all the time, rather there are many periods that packets are not communicated even in the connected mode. As such, continuously allocating and using of the radio resource(s) for whole time period in a connected mode may be ineffective and undesirable. In order to solve this drawback, the radio resource(s) may be allocated only when there is service data to be communicated.
Hereinafter, description of an RRC state of a terminal and a RRC connection method will be given in detail. The RRC state refers to whether the RRC of the terminal is logically connected to the RRC of the E-UTRAN, thereby forming a logical connection with the RRC of the E-UTRAN. If the RRC of the terminal forms a logical connection with the RRC of the E-UTRAN, this is referred to as an “RRC connected state.” Conversely, if there is no logical connection between the RRC of the terminal and the RRC of the E-UTRAN, this is referred to as an “RRC idle state.” When the terminal is in the RRC connected state and, accordingly, the E-UTRAN can recognize the existence of the corresponding terminal according to units of cells, the E-UTRAN can effectively control the terminal. On the other hand, the E-UTRAN cannot recognize a terminal that is in idle state. The terminal in idle state can be managed by the CN according to units of location areas or units of tracking (routing) areas, which are areas larger than the cell. Specifically, the existence of a terminal in idle state is only recognized according to units of large areas, such as location areas or tracking (routing) areas, and the terminal must transition into the connected state in order to receive typical mobile communication services such as voice or data.
When a user initially turns on the power of the terminal, the terminal first detects an appropriate cell and maintains its idle state in the corresponding cell. The terminal in idle state forms an RRC connection with the RRC of the E-UTRAN through the RRC connection procedure and transitions into the RRC connected state when the RRC connection needs to be formed. There are several instances in which a terminal in idle state is required to form the RRC connection. For example, an uplink data transmission may be required due to a call attempt by a user or the transmission of a response message in response to a paging message received from the E-UTRAN may be required.
Hereinafter, description of system information will be given. The system information may include all information required for a terminal to know for a connection with a base station. Accordingly, before the terminal attempts to connect to the base station, it should receive all system information and always have the most updated system information. In addition, considering that all terminals within one cell should know the system information, the base station periodically transmits the system information.
The system information may be divided into a Master Information Block (MIB), a Scheduling Block (SB), a System Information Block (SIB) and the like. The MIB serves to inform the terminal about a physical construction of a corresponding cell (e.g., a bandwidth, and the like). The SB serves to inform the terminal about transmission information of SIBs (e.g., a transmission period and the like). The SIB refers to a collection (or aggregate) of system information that are related to each other. For instance, some SIB may include information of neighboring cells only, and other SIB may include information about an uplink radio channel only used by the terminal.
In the related art, in order for a terminal to receive appropriate services without causing any trouble in a system, the terminal should always have the most updated system information. However, such system information needs to be received by a terminal which has newly entered into a cell, or a terminal which has been newly turned on in a specific cell. Accordingly, the base station would repeatedly transmit the system information. In this case, requiring the terminal to always receive the system information may cause a problem of unnecessarily wasting power to a terminal which has already received the most updated system information. Accordingly, it is necessary for the terminal to read system information only if the system information is actually modified.